Efficience de l’utilisation de l’eau chez le blé dur

Abstract

Water use efficiency is considered as an important characteristic associated with crops drought tolerance crops. The current thesis is based on the study of the physiological and molecular mechanisms of water use efficiency in durum wheat emphasizing on the involvement of stress response proteins (Aquaporins) in maintaining water status. Three experiments under semi-controlled conditions were conducted, ten varieties of durum wheat (Triticum durum Desf) were grown under three water regimes, 95%, 60% and 20% of the field capacity. In the first assay several morphological and physiological parameters related to the water status and associated with water use efficiency were measured: relative water content, water loss rate, osmotic potential, electrolyte leakage, stomatal conductance, leaf temperature, chlorophyll rate, leaf area, specific leaf weight, as well as the water use efficiency (WUE) and its components. The second experiment was devoted to the analysis of some physiological traits of Aquaporins response to water stress by applying the biochemical inhibitor HgCl2 “mercury chloride”. At the molecular level, the analysis of expression level of two Aquaporins isoforms TdPIP1.1 and TdPIP2.1 was carried out on wheat leaves and roots using a real-time quantitative PCR. The obtained results revealed highly significant differences among varieties for all measured parameters. This difference is mainly related to the level of stress imposed, for the majority of the studied parameters the effect of severe stress of 20% FC is mainly characterized by a decrease of the total dry matter as well as the quantity of water used which has led to an increase in the Water use efficiency for the majority of varieties. Moreover, stress induced a decrease in stomatal conductance, chlorophyll rate, relative water content, leaf area, osmotic potential and an increase in leaf temperature, electrolyte leakage, and specific leaf weight. In addition, the correlation analysis revealed significant correlations between WUE and the studied parameters such as total water consumption and stomata conductance which are considered as important traits to regard when studying WUE. The inhibition of the activity of the Aquaporins by HgCl2 highlighted the relationship between these proteins and the indicators of the water use efficiency (transpiration and stomata conductance).Our results showed that under mercury stress the varieties exhibited different resistance or tolerance capacities, which are strongly related to the different activities of the aquaporins (activation / inhibition) as well as to the adaptive capacities of the varieties. The results of the quantitative analysis of the aquaporin genes under severe stress conditions indicated that the TdPIP1.1 gene was negatively regulated in the roots, the abundance of the transcripts is more considerable in the roots of the variety Cirta. Conversely, a positive regulation of the TdPIP2.1 gene was emphasized in the roots of the variety Bousselam. This genotype may be suggested as tolerant genotype showing high values of water use efficiency under water stress conditions which is a result of the positive regulation of the aquaporin genes in the roots. These preliminary results provide a starting point for understanding the relationship between water use efficiency and Aquaporins activity under drought conditions.